Carbon nanotubes are unique carbon-based, molecular structures that exhibit interesting and useful electrical properties. There are two general types of carbon nanotubes, referred to as multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs). SWNTs have a cylindrical sheet-like, one-atom-thick shell of hexagonally-arranged carbon atoms, and MWNTs are typically composed of multiple coaxial cylinders of ever-increasing diameter about a common axis. Thus, SWNTs can be considered to be the structure underlying MWNTs and also carbon nanotube ropes, which are uniquely-arranged arrays of SWNTs.
Due to their unique electrical properties, carbon nanotubes are being studied for development in a variety of applications. These applications include, among others, chemical and bio-type sensing, field-emission sources, selective-molecule grabbing, nano-electronic devices, and a variety of composite materials with enhanced mechanical and electro-mechanical properties. More specifically, for example, in connection with chemical and biological detection, carbon nanotubes are being studied for applications including medical devices, environmental monitoring, medical/clinical diagnosis and biotechnology for gene mapping and drug discovery. For general information regarding carbon nanotubes, and for specific information regarding SWNTs and its applications, reference may be made generally to the above-mentioned patent documents, and also to: “Carbon Nanotubes: Synthesis, Structure, Properties and Applications,” M. S. Dresselhaus, G. Dresselhaus and Ph. Avouris (Eds.), Springer-Verlag Berlin Heidelberg, N.Y., 2001; and “T. Single-shell Carbon Nanotubes of 1-nm Diameter,” Iijima, S. & Ichihashi, Nature 363, 603–605 (1993).
Sensing chemical and biological species plays an important role in many industrial, agricultural, medical, and environmental processes. Detection of NO2 gas, for example, provides a crucial measure of environmental pollution due to combustion or automotive emissions. In industrial, medical and living environments, the amount of NH3 also needs to be closely monitored. Moreover, there is a growing need to detect biological species in a variety of biomedical applications. However, previously-used sensors typically must operate at elevated temperatures to enhance chemical reactivity, and often require long recovery times (if recoverable at all), poor reproducibility, and are applicable to the detection of a very limited range of chemical species.
Many electronic devices benefit from small-scale electronic circuits and arrangements, and also play in important role in a variety of applications. The size and electrical properties of nanotubes including carbon nanotubes make them potentially useful for such small-scale devices. However, previously-available nanotubes and nanotube approaches have been difficult to manufacture and implement in a variety of such applications.